A. Definitions of Terms
"Milk" means the lacteal secretion obtained by the milking of one or more females of a mammalian species, such as cow, sheep, goat, water buffalo, or camel. Broadly speaking, such milk is comprised of casein (a phospho-protein) and soluble proteins, lactose, minerals, butterfat (milkfat), and water. The amount of these constituents in the milk may be adjusted by the addition of, or the removal of all or a portion of, any of these constituents. The term "milk" includes lacteal secretion whose content has been adjusted.
Milk obtained by milking one or more cows is referred to as "cows milk". Cows milk whose composition has not been adjusted is referred to herein as "whole milk". It is comprised of casein, whey proteins, lactose, minerals, butterfat (milkfat), and water.
The composition of "cows milk" can be adjusted by the removal of a portion of or all of any of the constituents of whole milk, or by adding thereto additional amounts of such constituents. The term "skim milk" is applied to cows milk from which sufficient milkfat has been removed to reduce its milkfat content to less than 0.5 percent by weight. The term "lowfat milk" (or "part-skim milk") is applied to cows milk from which sufficient milkfat has been removed to reduce its milkfat content to the range from about 0.5 to about 2.0 percent by weight.
The additional constituents are generally added to cows milk in the form of cream, concentrated milk, dry whole milk, skim milk, or nonfat dry milk. "Cream" means the liquid, separated from cows milk, having a high butterfat content, generally from about 18 to 36 percent by weight. "Concentrated milk" is the liquid obtained by partial removal of water from whole milk. Generally, the milkfat (butterfat) content of concentrated milk is not less than 7.5 weight percent and the milk solids content is not less than 25.5 weight percent. "Dry whole milk" is whole milk having a reduced amount of water. It generally contains not more than five percent by weight of moisture on a milk solids not fat basis. "Nonfat dry milk" is the product obtained by the removal of water only from skim milk. Generally, its water content is not more than five weight percent and its milkfat content is not more than 1.5 weight percent.
Thus, the term "cows milk" includes, among others, whole milk, low fat milk (part-skim milk), skim milk, reconstituted milk, recombined milk, and whole milk whose content has been adjusted.
The term "whey proteins" means cows milk proteins that generally do not precipitate in conventional cheese making processes. The primary whey proteins are lactalbumins and lactoglobulins. Other whey proteins that are present in significantly smaller concentrations include euglobulin, pseudoglobulin, and immunoglobulins.
In the conventional manufacture of cheese, milk is processed to form a coagulum, which is further processed to produce a semi-solid mass called "cheese curd" (or "curd") and a liquid (whey). The curd contains casein, a small amount of lactose, most of the butterfat, minerals, and water. The whey contains whey proteins, most of the lactose, some of the butterfat, minerals, and water. The curd may be worked (e.g., stirred) and/or combined with certain flavor and taste producing ingredients, and/or ripened using bacteria to produce different varieties of "natural cheese".
One or more varieties of curd or natural cheese can be comminuted and mixed with an emulsifying agent to form, with the aid of heat, a homogeneous plastic mass called "processed cheese". Examples of processed cheese include: "process cheese", "process cheese food", "process cheese spread", and "process cheese product". The various types of processed cheeses are obtained depending on the processing conditions, the specific varieties of curds or natural cheeses used, and the additional ingredients added during the processing.
"Imitation cheese" is a food made in semblance of any natural cheese variety, processed cheese, or other foods made or natural or processed cheese, in which casein, caseinates, and/or safe and suitable non-milk ingredients, such as vegetable proteins and vegetable oil, replace all or part of the nutritive milk components normally found in the food being simulated.
Herein "buffer capacity" is the resistance of a system to pH change and is expressed in milliequivalents of hydrochloric acid absorbed per 100 grams of sample. Buffer capacity is measured by diluting 2 g of the milk, or the equivalent amount of process fluid with 100 mL of distilled water and titrating with 0.05N hydrochloric acid to pH 5.1 until that pH remains constant for at least twenty seconds. "Lactose" is expressed as grams of anhydrous lactose per 100 grams of sample.
B. The Problem This Invention Addresses
Natural cheese of the types used as bases for making processed cheese products, for example, Cheddar, stirred curd, Colby, Gouda, or Swiss, are made by coagulating milk, ripened with suitable lactic acid producing bacteria to a suitable acidity, with appropriate milk clotting enzymes, cutting the coagulum and cooking the resulting curd in its whey. The whey is drained from the curd, whereupon the curd may be cheddared or stirred while additional acid is produced by fermentation of lactose to lactic acid in the curd. The curd may or may not be washed with water. If cheddared, the curd is milled, whereupon it is salted and pressed into rectangular blocks or packed into barrels for maturing. The addition of lactic acid producing bacteria, ripening of the milk, cutting the curd, cooking the curd, stirring the curd, cheddaring the curd and salting the curd are all controlled to yield a product in which the residual lactose and the unused buffer capacity of the curd are balanced so that complete fermentation of the residual lactose in the curd to lactic acid will result in a cheese with the proper minimum pH for the particular market requirements, usually between 4.9 and 5.5.
The conventional processes for making natural and processed cheese utilize only casein. Whey proteins remain dissolved in the whey and are discharged as a by-product of the process. The whey proteins comprise about 14 to 24 weight percent of whole or skim milk's proteins and the nutritional value of the whey proteins is at least comparable to the nutritional value of casein. Accordingly, the loss of the whey proteins in the conventional cheese making processes limits the potential yields of such processes. The utilization of even a portion of the whey proteins in the manufacture of natural and processed cheeses is of great commercial importance.
C. Prior Attempts to Recover Whey Proteins
For the above-stated reasons, efforts have been made to design a process that would allow full utilization of the whey proteins in cheese making.
One approach is to recover whey proteins from the whey by drying, condensing, ultrafiltration, or reverse osmosis of the whey. The recovered whey proteins are then recombined with the cheese. Such processes are described for example in F. V. Kosikowski, Cheese and Fermented Foods, Edwards Brothers, Inc., Ann Arbor, Mich. 2 ed. 1977, pp. 451-458.
A problem with this approach is that some countries have laws which prohibit, for most types of natural cheeses, recombining separately recovered whey proteins with the curd. For example, in the United States whey proteins can be reincorporated into cheese curd only in the making of certain natural cheeses, such as skim milk cheese.
An additional problem associated with this approach is that the recovered whey constituents lack the physical and chemical characteristics required for the making of natural cheese. For example, the dried whey proteins can be sprinkled into the cheese curd. However, only a limited amount of whey proteins can be added to cheese curd in this manner without changing its desired properties. Accordingly, the whey proteins recovered from whey are not used to any significant extent in commercial processes for making natural cheese.
For these same reasons whey proteins recovered in this manner are not used to any significant extent in the commercial manufacture of process cheeses. Moreover, it is commercially feasible to add only limited amounts of such recovered whey proteins to process cheese spreads, process cheese foods, process cheese products, or imitation cheeses.
Another approach for utilization of whey proteins in cheese making is to co-precipitate them with the casein. One process for obtaining co-precipitates of casein and whey proteins from milk is disclosed in U.S. Pat. No. 3,535,304 and in the corresponding Australian Patent No. 403,065 (hereinafter referred to as the Muller patents). The Muller patents specify that the product resulting from this process should find acceptance in some forms of baby food, ice cream, coffee whiteners, small goods, biscuits, bread, breakfast cereals, and canned processed foods. The final product of the Muller process lacks the "functionality" for making processed and imitation cheeses, i.e., it does not have the functional characteristics that are required for making such cheese.
Other known processes for the production of co-precipitates of casein and whey proteins also result in products that, although useful for some applications, cannot be used as starting materials for making cheese.
A further approach for increasing the yields of cheese making processes by utilization of the whey proteins is by ultrafiltration of milk. It has previously been proposed to produce products suitable for conversion into cheese by altering the composition of whole or skim milk utilizing ultrafiltration or reverse osmosis. The milk is contacted with a membrane which permits the passage of water, lactose, and some minerals, but prevents the passage of casein, the whey proteins, butterfat, and some minerals. The selective concentration of milk results in the formation of retentate which contains whey proteins. When the retentate is coagulated by acid or rennet, it forms a coagulum which contains the whey proteins. If this coagulum is then subject to syneresis some of the whey proteins are lost in the expressed whey. One method for producing cheese by ultrafiltration of milk is disclosed in U.S. Pat. No. 4,205,090 (Maubois, et al.) and in Australian Patent Specification No. 477,399. According to this method, whole or skim milk is concentrated by ultrafiltration to about one fifth of its volume to give a product, sometimes called a "liquid pre-cheese", which is then manufactured by conventional means to give cheese. This method, however, is only suitable for making soft cheeses of the Camembert or Reblochon type and possibly some semi-hard cheeses. It cannot be used to produce harder cheese of the Cheddar, Colby, or stirred-curd type, because the water content of the pre-cheese is too high and the ratio of buffer capacity to lactose will not give the desired final pH in the product.
More recently, C. A. Ernstrom, B. J. Sutherland and G. W. Jameson described in an article entitled "Cheese Base for Processing: A High Yield Product from Whole Milk by Ultrafiltration" and published in Journal of Dairy Science, Vol. 63, 228-234, (1980), a process whereby the moisture content and pH of the final product can be controlled to any desired levels. This process provides a product, cheese base, which has a moisture content and pH appropriate for use in place of conventionally made natural cheeses in the production of process cheeses. In the Ernstrom, et al. process, whole milk of normal pH or acidified to pH 5.7 is concentrated by ultrafiltration to 40% original milk weight and diafiltered at constant volume until a desired ratio of lactose to buffer capacity is established. Then the retentate is further concentrated by ultrafiltration to 20% of the original milk weight. The retentates are then inoculated with cheese starter and incubated to completely ferment the residual lactose. Precise control of final pH is achieved by controlling the level of lactose through diafiltration.
The fermented retentate is converted in a batch manner to cheese base in a swept-surface vacuum pan evaporator. The cheese base can be used to replace the unripened natural cheese component of processed cheese as it has the same pH and gross composition as Cheddar cheese. The use of the batch evaporator is necessitated by the fact that the retentate upon fermentation forms a curd or coagulum. Such a product cannot be readily processed in any continuous flow evaporator. Accordingly, the overall process of Ernstrom, et al. is essentially a batch process.
Thus the prior attempts have been unsuccessful in devising a process for economical utilization of whey proteins in the manufacture of products with a composition of cheese. There is therefore an unsatisfied, long-felt need for a high-yield, efficient process for making such products. The present invention is concerned with improvements to the Ernstrom, et al. process just described, particularly in relation to the adaptation of the process to commercial use.